Abstract: The weight loss characteristics, evolution patterns of volatiles and morphology of solid product from co-pyrolysis of black liquor and petroleum coke were studied by a thermo gravimetric analyzer coupled with Fourier Transform Infrared Spectrometry (TGA-FTIR) and scanning electronic microscopy (SEM). The CO₂ co-gasification characteristics of black liquor char and petroleum coke were also investigated by thermo gravimetric analyzer (TGA). The results suggested that the pyrolysis reactions had proceeded independently during co-pyrolysis process at temperatures below 600 ℃. However, as the temperature exceeded 600 ℃, the release peak temperature of CO₂ and CO were shifted to low temperature zone, and the thermo gravimetric characteristics were changed in contrast with the separate pyrolysis. Moreover,the surface morphology of the solid products from co-pyrolysis had been changed dramatically at 800 ℃. Specifically, the sintering during pyrolysis of black liquor was inhibited by the presence of petroleum coke. Compared to the individual gasification, the carbon conversion and gasification rate had been greatly improved for CO₂ co-gasification due to the synergistic effect of the blends at 850 ℃. The overall carbon conversion were increased by 51.27%, meanwhile, the maximum gasification rate were improved by twice during CO₂ co-gasification process.